This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Cells are constantly exposed to exogenous and endogenous agents that threaten genome stability. However, cells have evolved various ways of protecting themselves. Checkpoints monitor DNA damage and DNA replication stress. DNA replication stress caused by various genotoxic agents such as hydroxyurea (HU) and methyl-methane sulfonate (MMS) activates replication checkpoint that slows down or stalls DNA replication. Several checkpoint proteins interact to monitor replication defects and activate repair processes to maintain DNA integrity. Recent works have shown that in addition to monitoring DNA integrity, the replication checkpoint proteins also monitor cellular morphogenesis during replication stress. In addition to the replication checkpoint proteins, several other groups of proteins also participate in resistance to HU and MMS in S. cerevisiae. However, their roles in genome integrity are just emerging. Certain genes in sphingolipids pathway have been found to play role in resistance to HU and MMS. The single inositol phosphosphingolipid phospholipase C gene ISC1 of S. cerevisiae confers resistance to HU and MMS. Deletion of the gene causes G2/M arrest in HU and MMS and this defect can be overcome by further deletion of SWE1 gene. In addition, genome-wide analyses have shown that ISC1 gene genetically interacts with DNA replication/sister-chromatid cohesion genes CSM3, CTF4, CTF8 and CTF18. Our goal is to understand the mechanism of action of Isc1 in cellular integrity upon exposure to genotoxic agents and also its interaction with the DNA replication/ sister-chromatid cohesion genes.